In the medical treatment of tumors there is a field of brachytherapy which involves a means for radiating the tumor itself or tissue very close thereto. The way in which the radiation is provided generally involves the placement of a very small diameter tube into the tumor. The tube forms a pathway to introduce a tiny portion of a radioactive material, e.g., iridium-192 to various positions in the tube for various dwell times to provide the amount of gamma radiation prescribed by the physician. The positioning of the radiation source is accomplished by a remote control device which permits the operator to be shielded from the radiation given to the patient. It, therefore, is readily understood that the machine must be able to accurately position the radiation source where it is intended to be. In the past a radiographic image was made of the radiation source controlled by an automatic stepping program, e.g., a program which commands movement of the radiation source a first given distance, remains for a given length of time, moves the source a second given distance, and remains for a given time, etc. The distance between radiation images was then measured on the radiograph and compared to the commands. A beginning location was normally set by puncturing the film wrapper by a pin at a known location. This technique for calibration has not been sufficiently accurate or reproducible to satisfy the physician. Accordingly, this invention provides an accurate means to verify the movement of the radiation source, now generally controlled by a computer and its software.
It is an object of this invention to provide a device for accurately measuring the movement of a radiation source by a high dose rate irradiating machine. It is another object of this invention to provide such a device that provides a radiograph of radiation spots superimposed on a scale. Still other objects will become apparent from the more detailed description which follows.